两种预氧化对氯消毒糖精DBPs转化的影响

Effect of Ozone and UV/H_(2)O_(2) Preoxidation on DBPs Formation Derived from Saccharin during Chlorine Disinfection

预氧化是饮用水净化的一种高级处理方法,其目标是减少有机物及其衍生污染,然而部分难降解有机物在氧化后转化为小分子物质,更易与氯发生反应,从而可能增加衍生消毒副产物(DBPs)的风险。以糖精(SAC)为模型前体物,通过模拟试验考察了净水工艺中臭氧及UV/H_(2)O_(2)预氧化对人工合成有机物在氯消毒过程中产生DBPs的影响,以及DBPs随供水时间的变化规律。结果表明,臭氧及UV/H_(2)O_(2)工艺可使抗氯氧化的SAC转化为易与氯反应的小分子有机物,产生更高含量的二氯乙酸(DCAA)、三氯乙酸(TCAA)、三氯甲烷(TCM)、二氯乙腈(DCAN)等DBPs,卤乙酸类DBPs含量升幅最大。DBPs的生成势(DBPFP)随着臭氧及UV/H_(2)O_(2)氧化时间的增加呈先增后减的趋势,在氧化接触15~20 min时DBPFP最大。采用氯消毒并连续2 d供水条件下,TCM、DCAA、TCAA和DCAN等DBPs的生成量随接触时间的延长而逐渐升高。臭氧与UV/H_(2)O_(2)预氧化对前体物的降解机理和效果不同,但均改变了难氯化物质在氯消毒阶段衍生DBPs特性,可见氧化接触时间等工艺条件选择不当会导致SAC生成DBPs的风险升高。

Preoxidation is an advanced treatment method for drinking water purification. Its goal is to reduce contamination caused by organic matters and their derived pollutants. However, some refractory organics are converted into small molecules after oxidation, which are more likely to react with chlorine,thereby increasing the risk of derivative disinfection by-products(DBPs) formation. Taking saccharin(SAC) as the model precursor, the effects of ozone and UV/H_(2)O_(2) preoxidation on DBPs produced by synthetic organic compounds during chlorine disinfection were investigated by simulation test, and the variation of DBPs with water supply time was explored. Ozone and UV/H_(2)O_(2) processes could convert chlorine-resistant SAC into small molecular organic compounds that could easily react with chlorine to produce more DBPs such as dichloracetic acid(DCAA), trichloracetic acid(TCAA), trichloromethane(TCM) and dichloracetonitrile(DCAN), and the content of haloacetic acid increased the most among all the DBPs. The formation potential of DBPs(DBPFP) increased firstly and then decreased with the increase of ozone and UV/H_(2)O_(2) oxidation time, and the maximum DBPFP was obtained when the contact time was 15-20 min. When chlorine disinfection was applied in water supply for two consecutive days,the yield of TCM, DCAA, TCAA and DCAN increased gradually with contact time. Ozone and UV/H_(2)O_(2) pre-oxidation had different degradation mechanisms and effects on precursors, but both of them changed the formation characteristics of DBPs derived from chlorine-resistant substances during chlorine disinfection. Therefore, improper selection of oxidation contact time and other process conditions may lead to an increased risk of DBPs generated by SAC.